What is the cost in dollars for the nails used to build a fence 80 meters long if it requires 30 nails per meter? There are 40 nails per box at a cost of 75 cents per box

4500 cent

Explanation:

From the question, we were told that

a fence 80 meters long requires 30 nails per meter.

1 metre fence = 30 nails

Then 80 meters long= ( 30 × 80)

= 2400 nails

Which means a fence 80 meters long will require 2400 nails in total.

We need to find the cost in dollars for the nails to build a fence 80 meters long.

We know that 40 nails per box will cost 75 cents per box.

(2400 nails/40 nail per box)= 60 box

Then 60 box will be needed to complete the fence.

the cost in dollars for the nails to build a fence 80 meters long= (60 box × 75 cent per box)=4500 cent

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.